Facsimile signaling system



Nov.'28, 1933. F. SCHROTER FAGSIMILE S IGNALING SYSTEM Filed Feb. 20, 1931' INVENTQR FRTZ SCHROTER 7%. ww/n/ ATTORNEY Patented Nov. 28, 1933 UNITED STATES FACSIMILE SIGNALING SYSTEM Fritz Schriiter, Berlin,

Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. 11., Berlin, Germa y, corporation of Germany Application February '20, 1931, Serial No. 517,136, and Germany February 26, 1930 4 Claims.

The present invention relates to a circuit arrangement adapted to prevent signal spread in short-wave telegraphy, especially in picture or facsimile telegraphy.

5 In United States Patent No. 1,914,898, granted on June 20, 1933 to me jointly with Wilhelm Runge, a method has been disclosed to eliminate disturbing or undesirable spread of signals in short-wave telegraphy, especially in high-speed telegraphy and picture 'telegraphy. Dash and dot, and black and white, respectively, are transmitted on waves of different lengths in such a manner that only the beginnings of both wavetrains will cause or control in the receiver the connection or disconnection of the recorder or inking current irrespective of extensions of the signals such as may be occasioned by multiple paths of the radiations. The invention hereinafter to be disclosed constitutes a further development of the above method by the aid of a circuit arrangement which, at the sending end.

permits the use of detuned keying or scanning while special means and ways are adopted only at the receiving end.

.Like the arrangement disclosed in the above referred to application, the circuit scheme hereinafter to be described in detail, for picture-transmission work, is also suited only for black-white contrast pictures or copies, while pictures involving shades or different stages of brightness do not come inside the scope of the invention. Hence, to transmit half-tones, recourse must priorly be had to a conversion of the copy or picture which permits of insuring intermediate impressions of blackening in well-known manner, for instance, by the screening (dot or line) method.

In what follows a description is given only of a case of facsimile transmission though, inside the scope-of the invention, the method to'be described could be utilized also for the expedited transmission of signals and spaces involved in various telegraphing systems and methods inasmuch as after the transformation into current impulses, say, a dash could be regarded as equivalent to a black or dark portion of the picture,

and a space to a light or lighter portion thereof.

Detuned keying of the transmitter, in the present connection, signifies the transmission well known in the prior art of two sufliciently difie'rthis connection, it is permitted to make a prethe record or re-created picture.

supposition which is sufficiently bome out by practical experience, i. e., that the heads of both waves are received at the receiving end with the same time intervals that have been present when scanning the copy atthe sending end between the instants of transition from light to dark, and vice versa.

For ultra-short picture signals or impulses, say, in scanning fine or thin lines, the wave-trains reaching the receiver equipment are apt to have a markedly variable characteristic. Owing to the propagation of short-wave radiations over diflerently, long paths, in case of high-speed transmission, in other words, of great speed of the film, a sequence of individual impulses sepa-JO rated by intervals may be recorded. If the rate of transmission speed is lower these impulses coalesce into an uninterrupted or permanent impulse. However, on account of the fact that they travel over difierent routes, impulses which ar-- rive together may also become extinct by action of interference or beat, and the result are gaps in However, in the circuit scheme hereinafter to be disclosed ways and means adapted to overcome the said.80 difliculty have been included. By the initiation of a glow-discharge which is released upon the starting of one wave, and which subsequently persists, permanent actuation of the recorder or inking relay is secured regardless of interference. pointsor interruptions in the picture signals.

The invention will be best understood when making reference to the following specification in connection with the accompanying drawing which illustrates one embodiment of the invention by way of example.

Referring now to the drawing, the waves picked up by the receiver equipment are suitably changed into intermediate frequencies by heterodyne action. Suppose the wave corresponding to black is ii, the one corresponding to white is )2. These waves may then be separated by means of filters l and 2, and they are caused to control and operate key or relay means 3 and 4 adapted to furnish a constant output potential irrespective of fluctuations in the field intensity. The arrangement is to operate in this manner that upon the arrival of Al, the light relay of the picture recorder means is caused to flash up with the result that the photographically sensitized recorder 9 paper is blackened from the respective point or instant. Upon the arrival of wave )2, this energization of the light relay is to be eliminated, in-

deed, its renewed operation is to be suppressed tor a certain length of time corresponding to the rent is thus allowed to flow from the positive pole of the battery 11 by way of resistance 9, glowdischarge gap 7--8 and further by way of resistance 12 shunted by a condenser 10 back to the negative pole. The. fall of potential occurring across resistor 9 is used for the purpose of causing a brightening of the light relay 22 by way of an amplifier 21 to produce markings'or blackenings upon a record surface associated with the light relay 22.

This excitation of relay 22 together with the, blackening of the photographic paper associated therewith continues until the wave )2 arrives, regardless of whether, owing to breaks or fading of wave ii the fall of potential across the resistance 5 is interruptedor not, owing to the continued action of the glow discharge in tube 5' when once the same has been initiated. When the wave )2 is-received, a sudden change in current is produced in the primary winding of transformer 13 which, by way of an amplifier tube 16, a coupling transformer 17 and another amplifier tube 18, causes a shock-like'charging up of the condenser 10. The cathodes 19 and 20 of tubes 16 and 18 are represented as being heated from a common battery 15. Owing to the .rise of potential produced across the condenser '10, inside the circuit containing the electrodes 7 and 8 of the glow-discharge relay 5','a reinforced fall of potential acts against the direct current voltage of battery 11. As a result the glow-discharge is discontinued and the fall of potential across the resistance 9 which excites the light relay 22 ceases. Hence, the recorder current is disconnected upon the arrival of wave )2. In order that repeated impulses of )2 which might originate from the same atmospheric causes as in the case of wave A1 may be prevented from occasioning additional charging of condenser 10, which, in the sense of the invention, is to become discharged gradually across the resistance 12, a negative biasing potential is obtained for the control grid of tube 16 by the aid of the adjustable contact 14 at the resistance 12. As long as current is flowing between the electrodes '7 and 8 of the glow-discharge relay, this negative biasing potential just has the correct value for the operation ofthe tube 16 functioning as an amplifier. However, if the voltage across condenser 10 or across the terminals of resistance 12 has been abruptly raised owing to the charge current caused by the starting or the in,- coming of the wave )2, then the control grid is blocked to an extent where renewed impulses of wave )\2 during a certain decaying time of the condenser 10 will be unable to affect tube 16 any longer. The decrease of potential of condenser 10 by way of resistance 12 must be regulated in accordance with the length of time within which lagging amplitudes. of wave k1 may still come in,

. this" end being attained "by suitable dimensioning.

of the capacity of condenser 10 and of the resistance 12, in other words, by. proper choice of the time-constant of the assembly. In this man- However, this blocking effect gradually decreases with the charge potential of condenser 10 and thereby insures the process of a time-limited counter-action against spreading of the wave A1.

Qther modifications and changes may suggest themselves to those skilled in the art to which the invention relates, and I, therefore, believe myself to be entitled to make and use any and all of such modifications as fall fairly within the spirit and scopeof the hereinafter appended claims.

Having now described my invention, what I claim and desire to secure by Letters Patent is the following: I

1. In a system for preventing spreading of signals wherein a plurality of diilerent frequency signals represent diflerent characters of trans= mission, a receiver system having portions thereof each responsive to a single one of said signals, a signalrecording device, a glow discharge means operative upon receipt of one of 'said signals for operating said recording device, means for maintaining the glow discharge device in an operative state irrespective of the per tence of said signals initiating the operation, and means operative upon receipt of the other of said signals for initiating a counter electromotive force to render the glow discharge device inoperative.

2. In a system for preventing spreading of recorded signals wherein spacing and marking impulses are produced each as signals of difierent frequency characteristics and which are each transmitted during the entire period of spacing or marking, means for receiving and separating each of said signals, a recording device, a glow discharge relay associated with said signal receiving means, means responsive to the receipt glow discharge device adapted to become operative to pass current upon receipt of one of said signals whereby the recording device is rendered operative, means for causing current to continue to flow through the glow discharge device subsequent to the initial signal so as to render the recording device permanently operative until the receipt of signals of diflferent frequency characteristic irrespective of the duration of the signals initiating the operation of the recording device, and means responsive to theirequency oi the second frequencycharacteristic for abruptly decreasing the operating voltage effective upon the glow discharge device to interrupt the current-.flow therethrough'and thereby render the recording device inoperative for a time period to each of said signals, a recording device, a i

said first received signals for rendering said re cording 'device operative, means for maintaining the operation of said recording device irrespective of the continuity of the signals initiating the operation thereof, means responsive to the signals of the second characteristic frequency, amplifying means connected with said second signal receiving means, a connection between said amplifying means and said glow discharge device for introducing into said glow discharge device during periods when signals of the second frequency characteristic are received a counter electromotive force for interrupting the operation of said glow discharge device; and rendering said recorder inoperative, and a capacity and resistance element associated with said amplifying system for neutralizing repeated impulses of the second wave characteristic.

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